摘要:

Infrared spectroscopy has been applied to the study of the kinetics of oxidation in high‐pressure dc‐sputtered amorphous silicon. The different spectra obtained during the evolution of the oxidation are processed by factor analysis. Two oxidation mechanisms have been found. Their associated infrared spectra and time evolution can be explained by a model that proposes the existence of a two‐level microstructure. The spectra associated with each one of the oxidation mechanisms seems to correspond mainly to SiO2, modified by the presence of surface modes.

ISSN:0021-8979    

DOI:10.1063/1.337223

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A quantum‐statistical theory of microwave and millimeter‐wave detection using superconducting tunnel junctions is developed, with a rigorous account of quantum, thermal, and shot noise arising from fluctuation sources associated with the junctions, signal source, and matching circuits. The problem of the noise characterization in the quantum sensitivity range is considered and a general noise parameter &THgr;Nis introduced. This parameter is shown to be an adequate figure of merit for most receivers of interest while some devices can require a more complex characterization. Analytical expressions and/or numerically calculated plots for &THgr;Nare presented for the most promising detection modes including the parametric amplification, heterodyne mixing, and quadratic videodetection, using both the quasiparticle‐current and the Cooper‐pair‐current nonlinearities. Ultimate minimum values of &THgr;Nfor each detection mode are compared and found to be in agreement with limitations imposed by the quantum‐mechanical uncertainty principle.

ISSN:0021-8979    

DOI:10.1063/1.337224

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The magnetic control of the filamentary current flow during avalanche breakdown in a semiconductor at low temperatures represents an interesting new principle of a magnetic field‐effect transistor. The power losses in such a device are minimized by using superconducting lines for the generation of the magnetic control field and for the interconnections. For such a hybrid concept, implementing semiconducting and superconducting components, the important performance characteristics are evaluated.

ISSN:0021-8979    

DOI:10.1063/1.337225

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The barrier height and ideality factor of Ti–Pt contacts onn‐type GaAs have been measured in the doping rangeNd=3.3×1016to 3×1018cm−3. The flat‐band barrier height, determined from capacitance‐voltage measurements, is found to be independent ofNdwhereas the effective barrier height for current transport, defined by the relation for thermionic emission, decreases rapidly atNd>1×1018cm−3. The results agree quite well with thermionic field‐emission theory.

ISSN:0021-8979    

DOI:10.1063/1.337226

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have obtained two‐dimensional hole gas with low temperature mobility as high as 3.8×105cm2 V−1 s−1at a density of 1×1011cm−2. The sample was grown on (311)A orientation. We give arguments to show that (100) orientation is not the optimum orientation for the growth of high purity materials.

ISSN:0021-8979    

DOI:10.1063/1.337227

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Correlation between the director reorientation and its consequent optical response time of the parallel‐aligned nematic liquid crystals was investigated. This optical decay time is found to depend on the phase retardation introduced by the liquid‐crystal layer. To verify theory, dependence of optical decay time on three parameters—liquid‐crystal thickness, wavelength, and birefringence (through temperature effect)—was demonstated. Taking the phase retardation dependence into consideration, the optical decay time measurement technique is a simple, convenient, and accurate method for characterizing the ratio of rotational viscosity and splay elastic constant of liquid crystals.

ISSN:0021-8979    

DOI:10.1063/1.337228

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

29Si nuclear magnetic resonance (NMR) spectra have been measured for amorphous hydrogenated silicon as well as amorphous‐microcrystalline mixed‐phase hydrogenated silicon using cross polarization and magic‐angle sample spinning.1H NMR spectra have been measured as well. The peak position of the29Si signal has been found to correlate well with the line shape of the1H NMR spectra, and mechanisms determining the position have been discussed.

ISSN:0021-8979    

DOI:10.1063/1.337229

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The activation energies characterizing a kinetic process are derived from the slopes of the Arrhenius diagrams obtained by plotting rate constants versus reciprocal temperature. Those rate constants correspond to the shifts along the time axis needed to superpose the successive isotherms. A general method based on Chebyshev interpolation is proposed for the optimization of the superposition of the experimental data points. This method is applied to determine the activation energies of the graphitization kinetics of the interlayer spacings of pitch coke and pyrocarbon samples.

ISSN:0021-8979    

DOI:10.1063/1.337230

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Plate impact experiments were conducted on AD‐85 alumina specimens (manufactured by Coors) in the low shock stress region. The experimental configuration consisted of impacting a thin flyer disc (either copper or alumina) on a relatively thick specimen disc (the target). A thin manganin stress gauge was placed at the back face of the specimen supported by a thick polymethylmethacrylate disc. After recording the initial shock at the specimen‐PMMA interface, the gauge showed an unusually fast compressional wave preceding the main release wave which originates at the flyer’s back surface. This wave appeared for all the shots with copper flyers and impact velocities resulting shock stresses in the 0–30 kb range. They did not appear when alumina flyers were used. Our explanation for the origin of this fast compressional wave is based on the possible occurrence of dilatancy in the specimen upon stress unloading.

ISSN:0021-8979    

DOI:10.1063/1.337231

出版商:AIP    

年代:1986

数据来源: AIP